Developmental Changes in Testicular Gonadotropin Receptors: Plasma Gonadotropins and Plasma Testosterone in the Rat

Abstract

The relationships between plasma gonadotropins, testicular gonadotropin receptors, and plasma testosterone were examined during neonatal life and throughout sexual maturation in the rat. The binding affinity of testicular LH receptors (2.4 X 10(10) M-1) was significantly higher than that of FSH receptors (2.1 X 10(9) M-1) at all stages of development. The concentration of FSH receptors in the testis reached a peak between 10-15 days of age, then fell to a constant level from 25-90 days. However, the testis content of FSH receptors increased continually with age and reached a plateau at day 60. Plasma FSH declined after birth to a nadir at 15 days, then rose rapidly to a peak at day 38, and fell to a plateau from day 50 through adult life. In contrast to the rapidly changing profile of plasma FSH during early maturation, alterations in plasma LH were less marked throughout development. Although a progressive rise in plasma LH concentration was observed between days 36-51, the simultaneous changes in testicular LH receptors and plasma testosterone were much more prominent. Testicular LH receptors showed a continuous increase in concentration and total number with advancing age and testis growth. The major rise in LH receptor concentration occurred between 15-38 days age, at the same time as the rise in plasma FSH concentration and the phase of rapid testicular growth. Plasma testosterone fell during the 8th-24th days after birth, then rose rapidly between days 35-55. The pubertal rise in plasma testosterone occurred about 15 days after testicular LH receptors began to increase and was coincident with the continuing rise in LH receptor content from day 35 until day 55 and with the progressive increase in plasma LH during this period. These observations have demonstrated that the early development of testicular FSH receptors in followed by a prominent rise in plasma FSH, with concomitant increases in testicular growth and LH receptor concentration. The resulting increase in gonadal sensitivity to LH could be responsible for the marked increase in secretion of testosterone which occurs during puberty in the presence of a relatively small change in the circulating LH concentration. The sequence of changes observed in gonadotropins and their testicular receptors is consistent with the view that FSH-induced testicular sensitivity to LH is an important factor in sexual maturation in the male rat.

Effects of induced hypoprolactinaemia in the ram : plasma gonadotrophin levels, LH and FSH receptors and histology of the testis

“…3c, d) A stimulating effect of bromocryptine treatment on FSH levels has also been reported in suckling ewes (Kann et al, 1977) and women (Seki et al, 1974 ;Nader et al, 1975). However, our results contrast with the increased release of FSH in hyperprolactinaemic rats (Voogt et al, 1969), dwarf mice (Bartke et al, 1977) and hamsters and also with the decreased secretion of FSH in men treated with bromocryptine (Lackritz and Bartke, 1980 (Rajaniemi et al, 1974 ;Charreau et al, 1977), as well as bromocryptine per se (Vermes and Telegdy, 1978) and FSH (Ketelslegers et a/., 1978) As suggested earlier (Barenton and Pelletier, 1980 ;Barenton, 1981) (Stolla et al, 1978) and mice (Bartke, 1974 …”

Age-Related Changes in the Serum Levels of Inhibin, FSH, LH and Testosterone in Holstein Bulls.

“…Aged bulls secreted more testosterone than younger bulls in the present study. Furthermore, since FSH increases the numbers of LH receptors in Leydig cells [8], Leydig cells of aged bulls might be more sensitive to LH. Further studies, for example, studies of age-related changes in the concentrations of LH receptors in testis, are needed to clarify the physiological roles of LH in age-related enhancement of the quantity and quality of semen in Holstein bulls.…”

Role of GnRH in the maturation of pituitary gonadotroph function

“…In male rats serum LH and FSH concentrations tend to be high during the neonatal (0-7 days of age) period (Döhler & Wuttke, 1974) (Ketelslegers et al, 1978). The FSH-dependent increase in LH receptors enhances the sensitivity of the testes to unchanged concentrations of serum LH and initiates a rise in the production of testosterone (Ketelslegers et al, 1978).…”

“…The FSH-dependent increase in LH receptors enhances the sensitivity of the testes to unchanged concentrations of serum LH and initiates a rise in the production of testosterone (Ketelslegers et al, 1978).…”